How do we know that Sauropods moved in herds? Well in this cartoon
of tracks
from the Davenport Ranch, Texas you can see how the tracks run parallel
much
like herds do of present animals.
The tracks tell us that a herd of about 23 sauropods are moving in
the same direction,
and about 5 theropods are most likely hunting among this herd.
(Lockley, 1991)